Bones, muscles and joints

Bones, muscles and joints make up the musculoskeletal system. They all grow and change throughout life. Injuries and various illnesses can damage bones, muscles and joints.

Musculoskeletal system structure

The adult human skeleton is made up of 206 bones. There are five main shapes of bones: long (such as the upper arm), short (such as the hand), flat (such as the ribs), irregular (such as the vertebrae) and sesamoid (such as the kneecap).

A joint is an area where two or more bones are in contact with each other. Cartilage provides cushioning inside joints (such as in the knee joint), or connects one bone to another (as in cartilaginous joints).

Ligaments join bones to other bones to strengthen joints.

Skeletal muscles run from one bone to another, usually passing at least one joint. They are connected to bones by tendons, which are the long thin ends of the muscles.

What is the function of bones, muscles and joints?

Bones give people shape. They hold the body upright, and also protect organs like the heart and the kidneys. They store the minerals calcium and phosphorus, and also contain bone marrow, where new blood cells are made.

There are different types of muscles and joints, each with different functions.

Skeletal muscle is muscle that you can consciously control. When your brain tells a muscle to contract, it shortens, pulling one bone towards another across a joint. Muscles work in pairs – when one shortens, a corresponding muscle lengthens. Physical activity maintains or increases the strength of skeletal muscles.

Smooth muscle sits in and around blood vessels and organs. You can’t consciously control smooth muscle. It helps regulate your blood pressure, airways and digestion.

The heart is made of special muscle called cardiac muscle. You can’t control it consciously. It contracts to make your heart beat.

Joints in the arms and legs are synovial joints which means they have fluid in them (synovial fluid)
so bones can move over each other.

Joints in the spine and pelvis are cartilaginous joints – they provide more stability and less movement.

There are also fibrous joints that allow no movement at all – just stability. You have fibrous joints in your skull.

Conditions and injuries related to the bones, muscles and joints

Many different conditions and injuries can affect the musculoskeletal system, such as: